1. Field of the Invention
The present invention relates to a vehicle brake device for braking a vehicle by the stepping manipulation of a brake pedal.
2. Discussion of the Related Art
Heretofore, in vehicle brake devices of this kind, where an impact of more than a predetermined magnitude is exerted on a vehicle at the time of a crash, collision or the like, the rearward displacements of an engine and the like cause a master cylinder to be displaced rearward. This may results in pushing up a brake pedal in a rearward direction, i.e., toward the driver, whereby an excessive load may be applied onto the driver's foot. To cope with this, there have been known those in which upon detection of a collision, brake oil in a master cylinder is forced to be flown to a reservoir tank to retract or withdraw the brake pedal away from the driver's foot (e.g., refer to patent documents 1 to 3 cited below).                [Patent Document 1] Japanese unexamined, published patent No. 2002-283987 (pp. 5-6, FIG. 3)        [Patent Document 2] Japanese unexamined, published patent No. 2000-272495 (pp. 2-4, FIG. 1)        [Patent Document 3] Japanese unexamined, published patent No. 10-305764 (pp. 2-4, FIGS. 1-2)        
In a vehicle brake device described in the patent document 1, when an impact beyond a predetermined magnitude acts on a vehicle, an oil pump is rotated to compulsorily make brake fluid (brake oil) in a master cylinder flow toward an ABS reservoir, and thus, a brake pedal is controlled to be withdrawn toward the master cylinder side, that is, toward the forward side of the vehicle.
Further, in a vehicle brake device described in the patent document 2, when an impact beyond a predetermined value acts on a vehicle, the atmospheric air is flown into a variable pressure chamber of a brake booster, and operating oil is drained to a reservoir from oil supply conduits through which oil pressures generated in a master cylinder are applied to wheel cylinders. Thus, a brake pedal is turned in a stepping direction.
Further, in a vehicle brake device described in the patent document 3, an oil pressure relief valve which is controllable by an electronic control unit in dependence on an output from an acceleration sensor is provided between a master cylinder operable by a brake pedal and brake cylinders for braking wheels, and upon detection of an acceleration indicating a collision of the vehicle, the oil pressure relief valve is opened to relive the brake pressure.
In each of the aforementioned vehicle brake devices, the brake pedal is withdrawn immediately upon detection of a collision, that is, the brake pedal is withdrawn before it is actually pushed up. Thus, it may occur that during the time period from a time point of the vehicle collision to another time point of the pushing-up of the brake pedal, the driver tries to keep his body balance, but cannot have anything to rely on.